An ultrasonic diagnostic apparatus is for obtaining displacement of the respective areas of the living body by applying pressure to an object to be examined using manual or mechanical method and imaging information related to the hardness of the tissues based on the obtained displacement, whereby enabling proper discrimination of the diseased tissues such as cancer tumors.
For example, a strain image is one of the hardness information of the tissues and is obtained by acquiring strain of the respective areas in the living body through performing spatial differentiation on a displacement distribution and imparting gradation sequence by hue or brightness in accordance with the degree of strain. However, a strain is a qualitative physical quantity depending on a compression quantity, thus the degree of strain is varied depending on the way of adding pressure. Therefore, the same tissue can be displayed by hue or brightness having greater value of strain just by adding greater pressure, which could lead to a false recognition of discrimination in tissues, depending on the experience or proficiency level of an examiner.
On the other hand, in Patent Document 1, the approach is proposed to obtain hardness property of the tissues that are not correlated with the compression quantity based on the strain image. More specifically, it is suggested to set region of interest ROI-1 and ROI-2 in the diseased tissue and surrounding tissues respectively in the strain image, and to make ratio ε1/ε2 of strain ε1 and ε2 in each ROI as hardness index. By such method, since the relative ratio of the strain between the two regions of interest does not depend on the compression quantity, it is possible to distinguish the difference between strain in the diseased area and its surrounding area almost quantitatively.
Patent Document 1: USPTO WO2006/013916